What causes endometriosis?

The exact cause is unknown. Most scientists think that it happens because of a process called retrograde menstruation.

Retrograde menstruation happens when tissue that lines the inside of your uterus flows out in the wrong direction during the period—through the fallopian tubes. While this process can occur in many healthy women as well, women with endometriosis experience it differently. The out-of-place tissue can attach and start growing on surfaces and organs in the pelvic region. This can cause pain and inflammation.  

Other possible theories on what causes endometriosis include:

  • The immune system not destroying endometrium cells outside of the uterus the way it should
  • Normal cells in the pelvic area changing into endometrial cells. This is called coelomic metaplasia
  • Endometrial cells forming outside of the uterus before birth, so that during puberty, those cells form endometrial lesions

Watch this video to learn about the inner workings of endometriosis and why it hurts.

What puts a woman at risk of endometriosis?

Possible endometriosis risk factors include: a family history of endometriosis, never giving birth, starting your period at an early age (before 11 years old), short menstrual cycles (fewer than 27 days), and long or heavy periods

Scientists aren't sure, but some possible endometriosis risk factors include:

No one demographic or ethnicity has been labeled as a risk factor for endometriosis.